The traditional way of assessing a nonsmokers’ exposure to secondhand smoke, by asking them to fill out a questionnaire, shows that respondents are often not aware about their likely contact with cigarette smoke. As a result, these nonsmokers could be unaware of having increased risk of lung cancer, heart disease and other smoking-related illnesses.

This has led to calls for more accurate ways of determining exposure to secondhand cigarette smoke, including by testing for the level of cotinine, a byproduct of nicotine, in blood samples.

Research into cotinine levels in the blood of more than 20,000 nonsmokers, found a significant increase in years of life lost across all levels of cotinine in the blood. The lowest levels of cotinine were associated with 5.6 years of life lost and the highest levels with 7.5 years of life lost. Though the study did not prove a cause-and-effect link, increased cotinine levels were associated with lung cancer, all cancers and heart disease,.

Along with pointing to a more accurate way to measure secondhand smoke exposure, the new study highlights the need for tighter smoking restrictions and increased preventive screenings for people more likely to have been exposed to secondhand smoke, the study authors said.

They point out that using cotinine level to measure exposure to secondhand smoke has important public health implications, because increasing the scope of smoke-free environments would likely decrease cotinine levels in the general population, and ultimately death.